Today, the Internet of Things (IoT) is considered a technology that is the most widely used in real life. In IoT, seamless data transmission and energy efficiency are important, and thus a low power network technology, such as a wireless sensor network, plays a crucial role. Also, in industry, a technology referred to as the Industrial Internet of Things (IIoT) has emerged as a new trend.
In the early 2000s, significant development occurred on ISA100.11a, Wireless HART, and other wireless technology standards, which have expandability and efficiency, that were suitable for industrial environments with numerous restrictive requirements. WirelessHART is a technology that has greatly improved the reliability and stability of wireless communication technologies, and WirelessHART employs Time Slotted Channel Hopping (TSCH) Media Access Control (MAC) protocol on the basis of the IEEE 802.15.4 standard. In 2012, the TSCH MAC protocol used in WirelessHART was adopted as a standard technology by being included in an IEEE 802.15.4e MAC amendment that improved on constraints of the existing IEEE 802.15.4-2006 standard. The IEEE 802.15.4e standard belongs to the license-free 2.4 GHz (Industrial Scientific and Medical) ISM band and is divided into 16 separate channels for use.
In the TSCH MAC protocol, nodes across a network are synchronized in time, enabling start times of slotframes to be matched and channel hopping information to be shared. The slotframe is repeated during an operation time, and a single slotframe includes a plurality of time slots. sleep, translate, and receive operations are performed for a single time slot. Channel hopping is a technology for transmitting and receiving data by varying the frequency used in each time slot, and which is provided to resolve problems associated with congestion.
Among steps of configuring the entire topology in the TSCH MAC protocol, there is a step of joining a synchronization for a network configuration. New nodes desiring to join the network need to receive an advertisement packet (ADV) that contains scheduling information that is transmitted by nodes that have already joined the network and required for the synchronization.
In order to use scheduling technology and channel hopping technology, which operate in the TSCH MAC, the synchronization technology is the essential and important factor. A node to join a network does not know scheduling information of the network until listening to the ADV message, and thus are limitlessly kept in a listening state. This lowers the energy efficiency of small devices that operate on batteries, shortening the period of actual operation, which can cause serious maintenance problems.
In order to enhance the productivity efficiency in a basic industrial environment, wireless communication is widely used. Wireless data exchanges for automation have been more frequently taking place. Most of the wireless communications used herein share a 2.4 GHz ISM band with each other, and interference caused by human and equipment movement may limitlessly extend a waiting state of a node that is listening in a particular channel.
In order to meet the reliability and stability, which are the most important characteristics in an industrial wireless network, there is need for a faster and more flexible synchronization strategy according to channel status and change.